Process for treating a hydrocarbon feed

ABSTRACT

The present invention concerns a process for the treatment of a hydrocarbon feed containing hydrogen and hydrocarbons including C 1  to C 4  hydrocarbons. The process employs two steps for recontacting gaseous and liquid phases and in which at least one of the recontacting steps is carried out in a column ( 30, 40 ) in which the gaseous and liquid streams are brought into counter-current contact.

The present invention relates to the field of the treatment of effluents from units for the conversion or refining of petroleum or petrochemicals which comprise hydrogen as well as hydrocarbons such as: methane, ethane, propane, butane, hydrocarbon fractions containing 5 to 11 carbon atoms (denoted C₅-C₁₁), and optionally heavier hydrocarbons such as hydrocarbons containing in the range 12 to 30 carbon atoms (C₁₂-C₃₀) or more, usually in small quantities.

In particular, it relates to a treatment of an effluent from catalytic reforming or from aromatization of fractions with a distillation range in the gasoline range (essentially containing 6 to 11 carbon atoms), which can be used to provide an aromatic reformate, a hydrogen-rich gas and a liquefied petroleum gas (or “LPG”) essentially comprising hydrocarbons containing three or four carbon atoms (propane and/or propylene and/or butane and/or butenes and/or butadiene, and mixtures thereof). The presence of C₃ and C₄ hydrocarbons in the catalytic reforming effluents is primarily linked to hydrocracking reactions which take place concomitantly with the dehydrogenation reactions.

The invention is also applicable to dehydrogenation effluents, for example butane, or pentane, or higher hydrocarbons, for example fractions essentially comprising hydrocarbons containing 10 to 14 carbon atoms, the olefins of which are used downstream for the production of linear alkylbenzenes.

The process in accordance with the invention may also be applicable to the hydrotreatment (and/or hydrodesulphurization and/or hydrodemetallization and/or total or selective hydrogenation) of all hydrocarbon cuts such as naphtha, gasoline, kerosene, light gas oil, heavy gas oil, vacuum distillate, or vacuum residue. More generally, it is applicable to any effluent comprising hydrogen, light hydrocarbons (methane and/or ethane), C₃ and C₄ hydrocarbons as well as heavier hydrocarbons.

PRIOR ART

The known prior art document U.S. Pat. No. 4,673,488 discloses a process for recovering light hydrocarbons from a reaction effluent containing hydrogen obtained from a reaction for the conversion of a hydrocarbon feed, which comprises:

-   -   passing the partially condensed effluent comprising C₅ ⁺         hydrocarbons, methane, ethane, propane, butane and hydrogen into         a vapour-liquid separation zone which comprises at least two         vapour-liquid separators and in which at least one vapour-liquid         recontacting step is carried out;     -   separating the effluent obtained after the vapour-liquid         separation zone into a hydrogen-rich gas stream and a stream of         liquid hydrocarbons;     -   passing the liquid hydrocarbon stream into a fractionation zone         comprising at least one fractionation column in a manner such as         to recover a stream of heavy hydrocarbons, an overhead vapour         and an overhead liquid; and     -   recycling a portion of the overhead vapour stream to said         vapour-liquid separation zone.

The document FR 2 873 710 is also known, which describes a process for the treatment of a hydrocarbon feed comprising a liquid hydrocarbon phase and a hydrogen-rich gaseous phase, in which:

a) the feed is separated into a liquid and a gas,

b) at least a portion of the gas is compressed and then brought into contact with at least a portion of the liquid in a manner such as to recover a liquid and a hydrogen-rich gas,

c) the liquid obtained from step b) is then fractionated to obtain at least: a stabilized liquid which is substantially free of LPG and lighter products, a light liquid effluent essentially comprising LPG and a gaseous stream which is recycled at least in part,

d) and in which at least one of the gaseous streams obtained from step a) or step c) is brought into counter-current contact with a non-stabilized liquid obtained from steps a) or b). The non-stabilized liquid is then supercooled to at least 10° C. below its bubble point at the contact pressure.

The term “stabilized” for a reformate (or another stabilized liquid in accordance with the invention) denotes a reformate (or other liquid) which has been distilled in order to eliminate the major portion, and generally substantially all of the compounds containing 4 carbon atoms or fewer (C₄ ⁻).

One aim of the invention is to provide an alternative process that can be used to maximize the recovery of hydrogen and C₃ and C₄ hydrocarbons.

SUMMARY OF THE INVENTION

Thus, the present invention concerns a process for the treatment of a hydrocarbon feed containing hydrogen and hydrocarbons including C₁ to C₄ hydrocarbons, in which:

a) the hydrocarbon feed is separated into a gaseous phase and a liquid phase containing hydrocarbons (4);

b) a first recontacting step is carried out by bringing the liquid phase into contact with a gaseous phase obtained from step c) at a temperature in the range −20° C. to 60° C., then the recontacting mixture is separated into a first gaseous effluent which is rich in hydrogen and a first liquid hydrocarbon effluent;

c) a second recontacting step is carried out by bringing the first liquid hydrocarbon effluent into contact with the gaseous phase obtained from step a) and a recycle gas obtained from step f) at a temperature in the range −20° C. to 60° C., then the recontacting mixture is separated into a second gaseous effluent and a second liquid hydrocarbon effluent;

d) the second gaseous effluent is compressed and said second gaseous effluent is sent to step b) as the gaseous phase;

e) the second liquid hydrocarbon effluent obtained from step d) is fractionated in a fractionation column in a manner such as to separate a gaseous overhead fraction and a liquid bottom fraction containing hydrocarbons containing more than 4 carbon atoms;

f) the gaseous overhead fraction obtained from step e) is condensed and a liquid phase containing mainly C₃ and C₄ hydrocarbons and a gaseous phase are separated and said gaseous phase is recycled to step c),

in which at least step b) or step c) is carried out in a column in which the gaseous and liquid streams are brought into counter-current contact.

The inventors have established that a process employing two recontacting steps in which the liquid and gaseous phases move in counter-directions between the two recontacting steps and in which one of the recontacting steps is operated in a recontacting (or absorption) column with counter-current movement of the liquid and gaseous phases in the column, improves the recovery of hydrogen and C₃ and C₄ hydrocarbons (the cut known as the LPG cut) contained in the treated hydrocarbon feed and thus a hydrogen-rich gas with an increased purity can be provided.

The term “recontacting” denotes an operation which can be used to extract compounds contained in a gaseous phase by means of a liquid phase which has an absorption capacity, by bringing the two phases into contact. As an example, recontacting may be carried out by bringing about direct contact by in-line mixing of liquid and gaseous phases, or in a recontacting device dedicated for said unitary operation.

The process in accordance with the invention may be carried out in different manners. In accordance with a first embodiment, step b) is carried out in a recontacting column in which the liquid phase is brought into counter-current contact with the gaseous phase and step c) comprises in-line contact and a separation which is carried out using a separator drum.

In accordance with a second embodiment, step c) is carried out in a recontacting column in which the first liquid hydrocarbon effluent is brought into counter-current contact with the gaseous phase obtained from step a) and the recycle gas obtained from step f) and step b) comprises in-line contact and a separation which is carried out using a separator drum.

In accordance with a third embodiment, steps b) and c) are carried out in a column in which the gaseous and liquid streams are brought into counter-current contact.

Preferably, in step b), contact is carried out at a pressure in the range 1.5 to 4.5 MPa.

Preferably, in step c), contact is carried out at a pressure in the range 0.8 to 3 MPa.

Preferably, step b) is carried out at a temperature in the range −10° C. to 10° C. This embodiment generally employs a cooling device such as a refrigeration device.

Preferably, step c) is carried out at a temperature in the range 20° C. to 50° C.

DETAILED DESCRIPTION OF THE INVENTION

Further characteristics and advantages of the invention will become apparent from the following description, given solely by way of non-limiting illustration and made with reference to the accompanying drawings, in which:

FIG. 1 is a flow diagram of a process in accordance with the prior art;

FIG. 2 is a flow diagram of a process in accordance with the invention, in accordance with a first embodiment;

FIG. 3 is a flow diagram of a process in accordance with the invention, in accordance with a second embodiment;

FIG. 4 is a flow diagram of a process in accordance with the inverse in accordance with a third embodiment.

Similar elements are generally designated by identical reference numerals.

The hydrocarbon feed which is treated by the process is, for example, an effluent from a catalytic reforming unit, dehydrogenation effluents, for example butane or pentane, or higher hydrocarbons, for example fractions essentially comprising hydrocarbons containing 10 to 14 carbon atoms, the olefins of which are used downstream for the manufacture of linear alkylbenzenes (generally termed LAB).

The process in accordance with the invention may also be applied to effluents from hydrotreatment units (hydrodesulphurization, hydrodemetallization, total or selective hydrogenation) of any hydrocarbon cuts such as naphtha, gasoline, kerosene, light gas oil, heavy gas oil, vacuum distillate, or vacuum residue. More generally, it is applicable to any effluent comprising hydrogen, light hydrocarbons (methane and/or ethane), LPGs (propane and/or butane) as well as heavier hydrocarbons.

Preferably, the process in accordance with the invention can be used to treat effluents obtained from catalytic reforming units.

FIG. 1 shows a flow diagram of a process for the treatment of a hydrocarbon feed in accordance with the prior art.

The feed containing a gaseous phase comprising hydrogen and a hydrocarbon phase including C₁, C₂, C₃ and C₄ hydrocarbons is sent via the line 1 to a gas-liquid separation device 2 which may be a gas-liquid separator drum which is known to the person skilled in the art.

The separation device 2 allows the recovery of a gaseous phase 3 and a liquid hydrocarbon phase 4, respectively from the head and bottom of said device 2. As indicated in FIG. 1, the gaseous overhead phase 3, which mainly contains hydrogen and light C₁, C₂, C₃ and C₄ hydrocarbons, may be divided into two streams 5 and 6. The stream 5 is recycled to a reaction unit located upstream, for example a catalytic reforming unit, as a recycle gas. The stream 6 of gas is compressed using a compressor 7 to a pressure in the range 0.8 to 3 MPa. Preferably, the gas 6 is sent to a separation drum in order to separate any traces of liquid hydrocarbons before being compressed.

The liquid hydrocarbon phase 4 obtained from the separator drum 2 undergoes a first recontacting step which consists of bringing said liquid hydrocarbon phase into contact with a gas phase 8 which has been compressed using a compressor 9. The gas phase is at a pressure in the range 1.5 to 4.5 MPa. The gas phase 8 is obtained from the second recontacting step which is described below. As indicated in FIG. 1, the first recontacting step is carried out by direct contact by in-line mixing of the liquid 4 and gaseous 8 phases. The gas/liquid mixture is then cooled to a temperature in the range −20° C. to 60° C. using a device 10 and sent to a separator drum 11 which is operated at the pressure of the gaseous phase 8, i.e. in the range 1.5 to 4.5 MPa.

Depending on the target temperature, the cooling device may be an air exchanger or a water exchanger or a refrigerating device.

The separator drum 11 separates a hydrogen-rich gaseous effluent which is evacuated from the process via the line 12, and a liquid hydrocarbon effluent which is sent via the line 13 to a second recontacting step.

The liquid hydrocarbon phase 4 is sent to the first recontacting step and the gas phase 6 is treated in the second recontacting step, while the liquid effluent produced in the first recontacting step is sent to the second recontacting step and the gaseous effluent obtained from the second recontacting step is used in the first recontacting step. Thus, the process is designed to be what is known as a “counter-current” process, in which the liquid hydrocarbon phase 4 obtained from the separator drum 2 moves in the opposite direction to that of the gaseous phase 6 obtained from the separator drum 2. As can be seen in FIG. 1, the liquid effluent obtained at the end of the first step for recontacting and gas/liquid separation is sent to a second recontacting step which uses the compressed gaseous phase 6 and a gaseous recycle phase 14 originating from the reflux drum of the stabilization column as described below. The liquid 13 and gaseous 6, 14 phases are brought into contact by in-line mixing and cooled with the cooling device 15, for example an air exchanger or a water exchanger or a refrigerating device, to a temperature in the range −20° C. to 60° C. The second recontacting step is carried out at the pressure of the compressed gas 6, namely in the range 0.8 to 3 MPa. The gas/liquid mixture is transferred to a separator drum 16 configured to separate a gaseous effluent containing hydrogen plus C₁-C₂ hydrocarbons and a liquid effluent containing mainly hydrocarbons containing 3 and more than 3 carbon atoms (C₃ ⁺ cut) with a minor quantity of light C₁ and C₂ hydrocarbons. Referring to FIG. 1, the gaseous effluent containing hydrogen and C₁-C₂ hydrocarbons withdrawn from the separator drum 16 via the line 17 is compressed by the compressor 9 in a manner such as to provide the compressed gas 8 which is brought into contact with the liquid hydrocarbon phase 4 (first counter-current recontacting step), as described above.

At the end of the second recontacting and separation step, a liquid hydrocarbon effluent 18 is obtained, the final product of the recontacting steps, which undergoes a stabilization step to recover a liquefied petroleum gas (C₃ and C₄ hydrocarbons) and a stabilized hydrocarbon cut containing 5 or more than 5 carbon atoms (C₅ ⁺ cut).

The liquid effluent 18 is heated before being sent to a stabilization unit. The stabilization unit comprises a distillation column 19 the bottom of which is provided with a circulation conduit equipped with a recirculation circuit comprising a reboiler (not shown) and an evacuation conduit 20 for the stabilized liquid effluent. The overhead gas from the column moves in a conduit 21 connected to a condensation system comprising a cooling device 22 for the overhead gas and a reflux drum 23. The condensed liquid separated at the reflux drum 23 is evacuated via the line 24 and is divided into two streams, one stream being recycled to the column 19 via the line 25, while the complementary stream which has not been recycled is evacuated from the process as a LPG stream via the line 26. The residual gas withdrawn from the head of the reflux drum 23, which has not been condensed and comprises C₃ and C₄ hydrocarbons and C₁-C₂ hydrocarbons, is evacuated via the line 14 and recycled to the second recontacting step with the liquid effluent 13 (obtained from the first recontacting step), as described above. The stabilized liquid effluent 20 recovered from the bottom of the distillation column 19 advantageously serves to supply an indirect heat exchanger system 27, 28 in order to preheat the liquid effluent 18 before it enters the distillation column 19. This thermal integration can thus be used to reduce the heating energy which has to be supplied to the reboiler in order to operate the distillation column 19.

FIG. 2 is a flow diagram of a first embodiment of the process in accordance with the invention based on the flow diagram of FIG. 1, and in which the second step for recontacting and separation of the liquid and gaseous phases is operated in a recontacting (or absorption) column 30. The recontacting column 30 may comprise perforated or bubble plates, or any other contacting plate, or may even be packed with structured or unstructured packing elements (Pall rings, Raschig rings or the like). As an example, the column may have in the range 5 to 15 theoretical separation plates, preferably in the range 7 to 10.

The liquid effluent 13 obtained from the separator drum 11 is sent to the head of the column 30, while the gaseous mixture comprising the compressed gaseous phase 6 and a gaseous recycle phase 14 originating from the reflux drum of the stabilization column is sent to the bottom of said column 30 in order to carry out a counter-current contact and so as to recover the gaseous effluent 17 containing hydrogen and C₁-C₂ hydrocarbons and the liquid hydrocarbon effluent 18 respectively overhead and from the bottom of the column. As can be seen in FIG. 2, the liquid hydrocarbon phase 4 is cooled by a cooling device 15 which may be an air exchanger or a water exchanger or a refrigeration device. The recontacting step is operated at a temperature in the range −20° C. to 60° C., preferably in the range −10° C. to 10° C., and at a pressure in the range 0.8 to 3 MPa.

Using a column 30 with counter-current contact of a non-stabilized liquid hydrocarbon phase 13 with low content of hydrogen and of light C₁ and C₂ hydrocarbons means that residual hydrocarbons contained in the vapour phase can be absorbed by the liquid phase. The liquid hydrocarbon effluent recovered from the bottom of the column 30 is the hydrocarbon stream which is supplied to the stabilization column 19, while the gas effluent 17 from the column head 30 which contains hydrogen and the residual hydrocarbons, essentially C₁ and C₂, is sent to the compressor 9 in order to supply the compressed gas 8 at a pressure in the range 1.5 to 4.5 MPa.

In accordance with the invention, said first recontacting step is carried out in-line, by bringing the compressed gas 8 into contact with the liquid hydrocarbon phase 4 obtained from the separator drum 2. Preferably, contact is carried out at a temperature in the range −20° C. to 60° C. (preferably in the range −10° C. to 10° C.). To this end, the gas/liquid mixing which was carried out in-line is cooled by the cooling device 10. The cooled mixture is sent to the separator drum 11 so as to separate a hydrogen-rich gas 12 containing C₁ and C₃ hydrocarbons and a liquid hydrocarbon effluent 13 which is recycled to the second recontacting step carried out in the column 30.

The step for stabilization of the effluent 18 in the distillation column 19 is similar to that described with reference to FIG. 1.

FIG. 3 represents another embodiment of the process of the invention, which differs from that of FIG. 1 by using a recontacting column 40 with a counter-current flow of liquid and gaseous phases in order to carry out the first step for recontacting and separation of the liquid and gaseous phases.

As can be seen in FIG. 3, the liquid hydrocarbon phase 4 collected from the separator drum 2 and the compressed gaseous phase 8 are sent at the head and at the bottom of the column 40 respectively. Before it is injected at the head of the column 40, the liquid hydrocarbon phase 4 is cooled with the device 41 to a temperature in the range −20° C. to 60° C., preferably in the range −10° C. to 10° C. Recontacting is carried out in the column at a pressure corresponding to that of the compressed gas 8, i.e. in the range 1.5 to 4.5 MPa.

The hydrogen-rich gas 12 also containing C₁ and C₂ hydrocarbons is withdrawn from the head of the column 40, while the liquid hydrocarbon phase 13 is sent to the second recontacting step where it is brought into contact with a gaseous stream resulting from mixing the compressed gaseous phase 6 and recycle gas 14 obtained from the reflux drum 23 of the stabilization column 19. As indicated in FIG. 3, contact of the liquid and gaseous phases is carried out by in-line mixing, at a temperature in the range −20° C. to 60° C. In order to reach the recontacting temperature mentioned, the gas/liquid mixture is cooled in the heat exchanger 15. Alternatively to the flow diagram of FIG. 3, in the case in which the liquid hydrocarbon phase 13 withdrawn from the bottom of the recontacting column 40 has a lower temperature than that of the gaseous mixture leaving the heat exchanger 15, said liquid hydrocarbon phase 13 is brought into contact with the gas mixture downstream of the exchanger 15.

In accordance with the invention, the gas/liquid mixture cooled to a temperature in the range −20° C. to 60° C. is introduced into the separator drum which separates a gaseous effluent 17 and a liquid effluent 18 which respectively supply the compressor 9 and the stabilization column 19.

The step for stabilization of the effluent 18 in the distillation column 19 is similar to that described with reference to FIG. 1.

FIG. 4 is another embodiment employing two recontacting columns 40, 30 to respectively carry out the first and second recontacting and separation steps.

As indicated in FIG. 4, the bottom of the recontacting column 40 is supplied with a compressed gaseous stream obtained from the recontacting column 30 and with a liquid hydrocarbon stream which is the liquid hydrocarbon phase 4 originating from the step for separation of the treated feed 1 by the separator drum 2. In accordance with the invention, the liquid hydrocarbon effluent 13 evacuated via the bottom of the column 40 is sent to the second recontacting step where it is brought into counter-current contact in the column 30 with the gaseous mixture 6 and 14 cooled in the exchanger 15. The liquid hydrocarbon effluent 18 which undergoes the stabilization step is withdrawn from the recontacting column 30, enabling a stream of C₃ and C₄ hydrocarbons and a stabilized hydrocarbon cut to be provided. The step for stabilization of the effluent 18 in the distillation column 19 is similar to that described with reference to FIG. 1.

Regarding the gaseous effluent 17, as was the case in the preceding embodiments, it is compressed then cooled before being supplied to the column 40 in order to bring it into counter-current contact with the cooled liquid hydrocarbon phase 4.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding application No. FR 15/01493, filed Jul. 15, 2015 are incorporated by reference herein.

EXAMPLES Example 1 (Comparative)

This Example illustrates the process of FIG. 1, in which two in-line recontacting steps are carried out, each recontacting step being followed by a gas/liquid separation step employing a separator drum.

The treated hydrocarbon feed is a reaction effluent obtained from a catalytic reforming unit and of which composition given in Table 1 below:

TABLE 1 Composition (kg/h) H2 7 200 C1 1 540 C2 2 540 C3 4 660 C4 branched 2 840 C4 linear 2 860 C5+ 178 360  Total Kg/h 200 000 

The feed was treated in a separator drum 2 at a temperature of approximately 40° C. and a pressure of approximately 0.33 MPa in order to provide a liquid hydrocarbon phase 4 and a gaseous phase 6.

The first recontacting step was carried out in-line by mixing a gaseous stream obtained from the second recontacting step compressed to a pressure of 3.3 MPa and the liquid hydrocarbon phase 4. The gas/liquid mixture was cooled to a temperature of 0° C. then separated in a separation drum 11 which provided a hydrogen-rich gas 12 and the liquid effluent 13.

The second recontacting step was also operated by in-line mixing of the gaseous phase 6, compressed to a pressure of 1.67 MPa, with a recycle gas 14 obtained from the reflux drum of the stabilization column 19 and the liquid effluent 13 withdrawn from the separator drum 11 of the first recontacting step. Gas/liquid contacting was carried out at a temperature of 43° C. and the mixture was sent to the separator drum 16. The liquid hydrocarbon effluent 18 was sent as a feed to the stabilization column operated to separate an overhead gas 21 containing C₃ and C₄ hydrocarbons and a stabilized liquid bottom fraction 20 containing hydrocarbons containing more than 4 carbon atoms. The overhead gas 21 was condensed in a reflux drum which was operated at a pressure of 1.6 MPa and at a temperature of 43° C. in a manner such as to provide a liquid stream 24 containing LPG (C₃ and C₄ hydrocarbons).

Example 2 In Accordance with the Invention

This example is based on the flow diagram of FIG. 3, in which the first step for recontacting and gas/liquid separation was carried out using a recontacting column 40 comprising 9 theoretical separation plates.

The treated feed was identical to that of Example 1; the composition is given in Table 1.

The recontacting column 40 was supplied overhead by the liquid hydrocarbon phase 4 cooled to a temperature of 0° C. and to the bottom with the gaseous mixture compressed to 3.3 MPa and at a temperature of 0° C.

The second recontacting step was operated by in-line mixing of the gaseous phase 6 compressed to a pressure of 1.6 MPa with a recycle gas 14 obtained from the reflux drum of the stabilization column 19, then by cooling the mixture to a temperature of 43° C. The cooled gaseous mixture was then brought into contact with the liquid hydrocarbon effluent withdrawn from the bottom of the column 40, the temperature of which was approximately 12° C. The cold gas/liquid mixture (approximately 25° C.) was sent to the gas/liquid separator 16.

Table 2 provides the percentage recovery of hydrogen, LPG and reformate for the various streams generated by the processes of Examples 1 and 2.

TABLE 2 Example 1 Example 2 (FIG. 1) (FIG. 3) Recovery of hydrogen in gas (12) 100.0% by wt 100.0% by wt Purity of hydrogen in stream (12) 93.6 (mol %) 95.3 (mol %) Recovery of C₃ and C₄ 52.9% by wt 82.1% by wt hydrocarbons in stream (26) Recovery of C₅ ⁺ hydrocarbons in 99.7% by wt 99.7% by wt stream (20)

It will be seen that the process of the invention using at least one step for recontacting employing a counter-current contact column significantly improves the percentage recovery of C₃ and C₄ hydrocarbons (LPG) in a manner such that these hydrocarbons are no longer evacuated with the hydrogen-rich gas; this essentially means that the purity of the hydrogen in stream 12 is increased.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. A process for the treatment of a hydrocarbon feed containing hydrogen and hydrocarbons including C₁ to C₄ hydrocarbons, in which: a) the hydrocarbon feed is separated into a gaseous phase (6) and a liquid phase (4) containing hydrocarbons; b) a first recontacting step is carried out by bringing the liquid phase into contact with a gaseous phase (8) obtained from step c) at a temperature in the range −20° C. to 60° C., then the recontacting mixture is separated into a first gaseous effluent (12) which is rich in hydrogen and a first liquid hydrocarbon effluent (13); c) a second recontacting step is carried out by bringing the first liquid hydrocarbon effluent (13) into contact with the gaseous phase (6) obtained from step a) and a recycle gas (14) obtained from step f) at a temperature in the range −20° C. to 60° C., then the recontacting mixture is separated into a second gaseous effluent (17) and a second liquid hydrocarbon effluent (18); d) the second gaseous effluent (17) is compressed and said second gaseous effluent is sent to step b) as the gaseous phase (8); e) the second liquid hydrocarbon effluent (18) obtained from step d) is fractionated in a fractionation column (19) in a manner such as to separate a gaseous overhead fraction (21) and a liquid bottom fraction (20) containing hydrocarbons containing more than 4 carbon atoms; f) the gaseous overhead fraction (21) obtained from step e) is condensed and a liquid phase (24) containing mainly C₃ and C₄ hydrocarbons and a gaseous phase (14) are separated and recycled to step c), in which at least step b) or step c) is carried out in a column (30, 40) in which the gaseous and liquid streams are brought into counter-current contact.
 2. The process as claimed in claim 1, in which step b) is carried out in a recontacting column (40) in which the liquid phase is brought into counter-current contact with the gaseous phase and in which step c) comprises in-line contact and a separation which is carried out using a separator drum.
 3. The process as claimed in claim 1, in which step c) is carried out in a recontacting column (30) in which the first liquid hydrocarbon effluent is brought into counter-current contact with the gaseous phase obtained from step a) and the recycle gas obtained from step f) and in which step b) comprises in-line contact and a separation which is carried out using a separator drum.
 4. The process as claimed in claim 1, in which steps b) and c) are carried out in a column in which the gaseous and liquid streams are brought into counter-current contact.
 5. The process as claimed in claim 1, in which in step b), contact is carried out at a pressure in the range 1.5 to 4.5 MPa.
 6. The process as claimed in claim 1, in which in step c), contact is carried out at a pressure in the range 0.8 to 3 MPa.
 7. The process as claimed in claim 1, in which step b) is carried out at a temperature in the range −10° C. to 10° C.
 8. The process as claimed in claim 1, in which step c) is carried out at a temperature in the range 20° C. to 50° C. 